1. Field of the Invention
The present invention pertains to heart valve prostheses and in particular, to bileaflet heart valve prostheses using pivotable valve members.
2. Description of Related Art
Various types of heart valve prostheses have been developed which operate hemodynamically, that is, by the pumping action of the heart. Although, upon cursory observation, such heart valve prostheses appear to be relatively simple mechanisms functioning merely as check valves, considerable effort has been expended in their design and improvement, due principally to their life support function.
Heart valve prostheses are movable between an open position to allow blood flow in a downstream direction and a closed position to minimize regurgitation of blood in an upstream direction. Because hemodynamic energy alone is relied upon for proper operation of the heart valve between opened and closed positions, it is generally desirable to reduce friction losses in the heart valve which would needlessly burden the cardiac system. The interfitting occluders and heart valve body, which is typically annular in configuration, are usually designed with a certain amount of "play". A relatively loose fitting engagement between the occluders and the valve body reduces friction losses and is one technique employed to eliminate the possibility of binding of the occluders.
Considerable attention has been paid to bileaflet heart valves of the type having a pair of opposed leaflets which are generally semicircular in shape and which have abutting diametrical edges that are joined together during valve closing. A number of different arrangements have been proposed for pivotally mounting leaflets within an annular valve body and, despite efforts which have been devoted to the operational reliability and low friction operation of these devices, further improvements can be made. For example, U.S. Pat. No. 4,443,894 provides leaflet occluders having generally opposed upstream and downstream generally flat surfaces and which are generally wedge-shaped in cross-sectional profile. The leaflets are pivotally mounted within valve body depressions by hemispherical projections or mounting ears. Outwardly extending from the leaflets, adjacent the diametrical edge thereof. The depressions in the valve body are shaped with a generally spherical contour for cooperation with the spherical projections. Over the countless number of operations of a heart valve, the projections and depressions are subjected to wear. For the reasons set forth in U.S. Pat. No. 4,689,046, spherical projections and depressions are susceptible to significant amounts of "play" in directions lying in the plane of the leaflet and extending generally perpendicular to the diametrical edge thereof. It has been observed that relatively small amounts of wear adjacent the tip of the spherical projection or the corresponding center portion of the recess results in a significant amount of lateral play, even for relatively minute amounts of increased "end play" that is, in directions generally parallel to the diametrical leaflet edge and extending along the hinge points of a leaflet. As a result of this lateral play, the motion and the sequence, especially the synchronous cooperation of the leaflets becomes less well defined. As a result, performance of the leaflet may become erratic, as is evidenced, for example, by an asynchronous closure of the valve. While in general, prior art heart valves have proven to be very reliable, and have in general been shown to have a projected life expectancy exceeding that of the patient, it is desirable to achieve increased margins of safety by providing a prosthesis which substantially exceeds reliability and performance requirements.